The neural crest is a transient population of vertebrate embryonic precursor cells that generates a wide variety of cell types of peripheral neurons and glia, endocrine cells, pigment cells and elements of the craniofacial skeleton. Because neural crest development involves nearly all of the basic processes common to embryonic development generally, the neural crest has been extensively utilized as a model system to study embryonic cell diversification. In addition, a large number of clinically relevant conditions in humans result from miscues during neural crest development that can range in severity from functional inconvenience to catastrophe. Lastly, because neural crest is strictly a vertebrate embryonic tissue, understanding neural crest development has important revolutionary implications. Taken together, elucidating how neural crest development is regulated is important in order to understand the generation of a variety of functionally significant cell types, to provide insights into embryonic development generally, and to understand and ultimately relieve a number of adverse human afflictions that involve the neural crest and neural crest- derived cells. We propose to systematically screen for zebrafish mutations that disrupt neural crest development as a means to ultimately identify the molecular mechanisms that control neural crest development. We will identify mutations by monitoring crestin gene expression as a marker for neural crest cells, focusing on four different stages of embryogenesis that correspond to major events in neural crest development, first by in situ hybridization and ultimately using a mutagenized crestin-GFP transgenic line. All identified mutant lines will then be characterized by analyzing the expression of a large battery of neural crest sublineage- and derivative- specific molecular probes. Mutants will be classified on the basis of these results and further characterized by complementation analysis and linkage mapping. The isolation and initial characterization of large numbers of mutations that disrupt neural crest development will provide an important resource for the research community and be invaluable for elucidating mechanisms that regulate neural crest development.